Mark, Perry and Ken started walking at the same time from the same starting point round a circular track. Ken walked in the clockwise direction. Mark and Perry walked in an anti-clockwise direction. Ken took 6 min to complete each round. He met Mark after every 2 minutes. He met Perry after every 5 minutes. The three friends kept to their respective speeds throughout their walk.
- How many rounds did Ken complete in 1 h?
- When Ken and Mark met again at the starting point after 1 h, Perry had completed 2.4 km. Find the circumference of the circular track in metres.
(a)
1 h = 60 min
Number of rounds that Ken completed in 1 h
= 60 ÷ 6
= 10
(b)
Ken took 6 min to complete 1 round
1 min =
16 of circular track = 1 u
6 min =
66 of circular track = 6 u
Ken's distance is the repeated identity.
Make Ken's distance the same.
Ken's distance : Mark's distance
2 : 6 - 2
2 : 4
Ken's distance : Perry's distance
5 : 6 - 5
5 : 1
Ken |
Mark |
Perry |
2x5 |
4x5 |
|
5x2 |
|
1x2 |
10 |
20 |
2 |
The distance of Ken is the repeated identity.
LCM of 2 and 5 = 10
In 1 h
Ken's rounds : Mark's rounds : Perry's rounds
10 : 20 : 2
Distance that Perry completed in 1 h = 2.4 km
2 rounds = 2.4 km = 2400 m
1 round = 2400 ÷ 2 = 1200 m
Circumference of the circular track = 1200 m
Answer(s): (a) 10; (b) 1200 m